<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- 
        一行文本：
            在320~375屏中：fs:15px;
            在375~414屏中：fs:18px;
            在414~480屏中：fs:21px;
            在>480屏中   ：fs:24px;
     -->
     <!-- <style>
         @media screen and (min-width:320px) and (max-width:375px){
             .box{
                 font-size: 15px;
             }
         }
         @media screen and (min-width:375px) and (max-width:414px){
             .box{
                 font-size: 18px;
             }
         }
         @media screen and (min-width:414px) and (max-width:480px){
             .box{
                 font-size: 21px;
             }
         }
         @media screen and (min-width:480px){
             .box{
                 font-size: 24px;
             }
         }
     </style> -->

     <!-- <style>
        @media screen and (min-width:320px) {
            .box{
                font-size: 15px;
            }
        }
        @media screen and (min-width:375px){
            .box{
                font-size: 18px;
            }
        }
        @media screen and (min-width:414px){
            .box{
                font-size: 21px;
            }
        }
        @media screen and (min-width:480px){
            .box{
                font-size: 24px;
            }
        }
    </style> -->

    <style>
        @media (min-width:320px) { .box{font-size: 15px;}}
        @media (min-width:375px) { .box{font-size: 18px;}}
        @media (min-width:414px) { .box{font-size: 21px;}}
        @media (min-width:480px) { .box{font-size: 24px;}}
    </style>
</head>
<body>
    <p class="box">我是一个孤独的DIV</p>
</body>
</html>